1. Field of the Invention
The field of the invention is computer peripheral equipment and, in particular, means for rendering existing disc memory equipment compatible with external solid state memory devices.
Larger computer systems frequently employ an external mass memory to augment their internal memory systems. Historically, such a memory has taken the form most frequently of a rotating disc file. The latter employ rotating discs and recording heads which magnetically record information in magnetic coatings on the rotating discs. The stored information occupies a very small magnetized area on the disc and has the advantage of constituting an extremely inexpensive system. Such disc file external memories have the important drawback of being mechanical and thus inherently less reliable than solid state devices and further suffer from limited speed of operation due to the mechanical rotation of the mechanical discs.
For every memory system, regardless of type, the computer must know where each specific bit of information is stored. In a disc memory system, the location of the information stored in the memory is identified by track address (usually carried on a number of parallel wires with signals corresponding to binary track address) and sector address. The latter is a small segment of track (i.e., 360.degree.) which may be divided into numerous sectors usually ranging between 8 and 256. A given sector is associated with a particular number starting from an arbitrary origin fixed with respect to the disc rotation. In a track divided into eight sectors of 45.degree. each, sector No. 1 would be from 0.degree. to 45.degree., sector No. 2 from 45.degree. to 90.degree., and so on.
The exact bit is identified through its sequential position with respect to the beginning of the sector in which it is located. Thus, track information is issued instantly in parallel, and sector and bit information depends on the time of occurrence with respect to the origin pulse and relative to the beginning of the sector.
In conjunction with external memory systems utilizing the disc arrangement described hereinabove, interface elements called "disc controllers" are employed to afford access to a disc by the computer. Normally, a disc controller receives track and sector address information in parallel from the computer, and observes timing signals generated by the disc designated origin clock, sector clock, and bit clock, in determining when the disc is ready. At that point, the controller turns to the computer and requests write data from the computer memory. In the inverse operation, i.e., when the computer requests certain read data, identified by track, sector, and word address, the controller waits for the proper time when such information is available from the disc, collects it, and transmits it to the computer memory.
Recently, advances in integrated circuit solid state electronics have rendered it economically feasible to produce solid state memories in commercial quantities. In these memories, each bit is stored in an individual electronic circuit. Two of the most successful types of solid state memories are a random access memory comprising numerous (e.g., on the order of thousands) individual small electronic circuits and a block-oriented random access memory comprising a multiplicity of individual "bucket brigade" delay lines utilizing charge coupled devices. Because of their increasing economic and commercial feasibility, there has been a trend toward the use of such solid state memory devices as external mass memories associated with computers. This, however, has had the disadvantage of requiring the development of expensive interface circuitry and programming permitting the computer to "understand" how to use the new types of mass memories.
Thereore, there has been a felt but unfulfilled need for a system permitting solid state memory devices to be employed as mass external memories for computers and peripheral apparatus arranged to utilize existing external disc memories, without requiring installation of extensive new interface circuitry and programming.